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Steam is having its own sale but these are $15 AUD on that. If you buy from Amazon (you can use your Australian credit card, just add an American shipping address - it worked for me) you get the same thing for a fraction of the price.
Years 1-4
http://www.amazon.com/LEGO-Harry-Potter-Years-Online/dp/B008…
Years 5-7
http://www.amazon.com/LEGO-Harry-Potter-Years-Online/dp/B008…
I don't know how long this will last. So if you want it, get it quickly.
Also worked for me with selecting an American shipping address.
For comparison, the game is currently on sale for $24.00 on Steam. That's after 50% off!